Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Fair Value Financial Assets and Liabilities Measured on Recurring Basis

The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy:

	December 31, 2015
	Level 1		Level 2		Level 3		Total
	(in thousands)
Financial Assets
Money market funds	$	148,604	$	—	$	—	$	148,604
Restricted money market funds		225		—		—		225
Total financial assets	$	148,829	$	—	$	—	$	148,829

	December 31, 2014
	Level 1		Level 2		Level 3		Total
	(in thousands)
Financial Assets
Money market funds	$	27,847	$	—	$	—	$	27,847
Restricted money market funds		75		—		—		75
Short-term investments		—		10,010		—		10,010
Total financial assets	$	27,922	$	10,010	$	—	$	37,932
Financial Liabilities
Preferred stock warrant liabilities	$	—	$	—	$	1,810	$	1,810

Schedule of Remeasured Preferred Stock Warrants to Fair Value using OPM and/or PWERM Models

At December 31, 2014 and 2013, the Company remeasured the preferred stock warrants to fair value using the OPM and/or the PWERM models with the following assumptions used in the OPM:

	Year Ended December 31,
	2014	2013
Expected term (in years)	1.2 – 2.5	2.5 – 3.1
Expected volatility	69 – 86%	66 – 70%
Risk-free interest rate	0.3 – 0.6%	0.4 – 0.7%
Expected dividend rate	—  %	—  %
Discount for lack of marketability	19.5 – 24.3%	23.7% – 25.8%

Summary of the Changes in the Estimated Fair Value of the Company's Preferred Stock Warrant Liabilities

The following table provides a summary of the changes in the estimated fair value of the Company’s preferred stock warrant liabilities, which were measured at fair value on a recurring basis using unobservable inputs (Level 3) until their exercise (in thousands):

	Year Ended December 31,
	2015			2014		2013
	(in thousands)
Fair value, beginning balance	$	1,810		$	430	$	171
Fair value of preferred stock warrants exercised		(19,253	)		—		57
Change in fair value of preferred stock warrants		17,443			1,380		202
Fair value, ending balance	$	—		$	1,810	$	430